Magnetic current-control devices



. Dec. 6, 1960 H.E.DARUNG MAGNETIC CURRENT-CONTROL DEVICES Filed April4, 1957 Horde e liparlinj W014i. 1 W

ATTORNE vices. amplifying apparatus of the type which includes output2,963,639 "MAGNETIC CURRENT=CONTROL DEVICES Horace E.-Darling, NorthAttleboro, Mass, assignor to The Foxboro Company, Foxboro, Mass.

Filed Apr. 4,1957, Ser. No. 650,706

Claims. or. 323- 89) This invention relates to magnetic current-controlde- More particularly, this invention relates to slgnal windings woundon saturable magnetic corematerial and used to vary the flow of currentfrom-an A.C. energizing source in accordance with signals fed to'a-control winding on the core.

11H such .magnetic amplifying equipment provided here- "tofore,th'erehas been a problem in achievingdesired high-gain characteristicswithout introducing instabihty, e.g. continuous oscillation, hunting,etc.

jgized by a single-frequency source of current, the saturationcharacteristics of the magnetic material produce sharp discontinuitiesin the current flow'resultingin' the development of a wide range ofharmonic components.

Such harmonic components are, of course, coupled from the outputwindings to the amplifier control winding which also is wound on themagnetic core. From the control winding, the harmonic components feedback to the output circuit of the equipment which drives the magneticamplifier, for example a preceding stage of amplification, and disturbthe functioning of the system. The problem is particularly acute whenthe system is arranged to have high amplification gain, since anydisturbance will be greatly magnified and will tend to produceoscillations and other series effects detrimental to proper functioningof the apparatus.

The problem can be alleviated to some extent by inserting a loss elementsuch as a resistor in series with the magnetic amplifier controlwinding. Theresistor tends toabsorb the harmonic components so that theycannot disturb the functioning of the system. However, a resistor largeenough to eliminate undesired interaction effects will normally alsodecreasethe system amplification gain a substantial amount.

stantially affecting the flow of signal current into the magneticamplifier control winding. Asa result, interaction disturbances areminimized, and the system can be an ranged to have high gain without the'oscillation and hunting difficulties, previously encountered.

Theshort-c'ircuit'ed winding arrangement is particularly suited formagnetic amplifiers of the'balanced, fullwave ;-.type. In this'type of-amplifier,-as described hereinbelow in det-ail, there are two A.C.energized output windings, each wound on'a separate magnetic core, and'each ener- 1=gi26d on alternate half-cycles of the"A.C. supply. 7 Ithas *been found that a short-'circuited windingw'ound'around both of thecores not onlymim'mizes thedisturbing' efiects of interaction discussedabove, but also improves the performance of the amplifier, e.g.increased gain. Inthis regard, it is believed that the close couplingbetween the cores providedby the short-circuited winding produces aresetting action which conditions the magnetic material of each coreduring the half-cycle that its output winding is not energized. Thisresetting-action apparentlyaugments the flux produced 'by the magneticamplifier "control winding, and thereby improves the efiiciencyofcontrol exercised over the flow of current through the A'.C. energizedoutput windings.

Accordingly, it is an object of thepresent invention to provide magneticamplifying apparatus that is superior to such apparatus-providedheretofore. It is a further object of this invention to provide suchapparatus having improved stability characteristics. It is a still'furtherobject to provide a magnetic amplifier that is economical toconstruct yet capable of high-gain performance. Other objects, aspectsand advantages of this invention will be pointed out in, or apparentfrom,-the following description of preferred embodiments consideredtogether with the accompanying drawings, in which: I

Figure 1 is a schematic diagram of atwo-stage magnetic amplifierconstructed in accordance with the present invention;

Figures 2A and 2B are pictorial representations of the voltage waveformsin the output windings of the amplifier of Figure 1; and

Figure 3 is a schematic diagram of a modified form of magneticamplifier.

Referring now to Figure 1, there'is diagrammatically shown a magneticamplifier having two stages generally indicated at'lil and 12. The-firststage of amplification comprises a pair of separate identical toroidalcores 14 and 16 of saturable magnetic material surrounded by a number ofwindings as will be described. Although these windings are shown indifferent positions around the cores, 'it will be understood that inpractice the windings are' all evenly distributed about the cores in amulti-layer arrangement.

Wound about each of the cores'14 and 16 respectively is a correspondingpair of output gate windings 18 and 20 connected together at acommonpoint 22. These windings are energized through rectifiers 24 and 26which areconnected to the opposite ends of one secondary winding 28 of apower transformer generally indicated at 30. The primary winding32 ofthis transformer is connected to a source of AC. energizing potential,e.g. the usual volts, 60 cycle power line. The secondary-winding28includes a center-tap connection 34 which is connected through a controlwinding 36 of the second stage of amplification 12 back to the commonpoint 22 between the gate windings 18 and 20.

Accordingly, the output circuit for the first stage 10 is a balancedfull-wave arrangement wherein the gate windings 18 and 20 are energizedon alternate half-cyclesof the AC. energizing source. During the firinghalf-cycle foreither gate winding, the voltage across the winding buildsup sinusoidally (references 38 and 40 of Figures 2A and 2B) until themagnetic material of the corre sponding core saturates. At this point(references 42 and 44, Figures 2A and 2B) the voltage across the windingdrops essentially to zero, and current flows through the control winding36 of the second stage 12 for the remainder of the half-cycle. Therectifiers 24 and 26 are polarized so that the current flowing throughthe control winding 36 will always be in the same direction, and'theaverage magnitude'of this current varies in accordance with changes inthe point at which saturation occurs.

The point in the energizing cycle at which-saturation {of cores 14'and16 occursisdetermined primarily" by the wound around both of the cores.

46 which encircles both of these cores. In addition, the saturationpoint is set for a given input current level by a conventional biaswinding 48 wound around both the cores and supplied with DC current froma rectifier power supply generally indicated at 50.

To avoid the disturbing eifects of harmonics generated in the gatewindings 18 and 20, the cores 14 and 16 also are provided with ashort-circuited winding 52 which is This winding, because it isinductively coupled to the magnetic fiux paths of the (amplifier cores,absorbs the harmonic components generated 1n the gate windings due tothe sharp discontinuities of current flow through these windings.Furthermore, the current flowing in the short-circuited winding whileeither one of the gate windings is energized pro 'duces flux in the coreassociated with the other gate winding, and this flux aids the controlwinding 46 in conditioning that core for proper operation during thenext succeeding half-cycle of the A.C. energizing source.

The second stage of amplification 12 comprises a pair of identicaltoroidal cores 54 and 56 of saturable magnetic material arranged in amanner similar to cores 14 and 16 previously described, and biased tothe proper magnetic operating conditions by the interstage circulatingcurrent passing through the control winding 36. The cores 54 and 56carry respective gate windings 58 and 60 which are connected withrectifiers 62 and 64 as a balanced full-wave output circuit energized byanother secondary winding 66 on the transformer 30. The center tap 68 ofthis secondary winding is connected through a load resistor 70 and anegative feedback circuit 72 to the common point 74 between the gatewindings 58 and 60.

The output signal of the amplifier is smoothed by a filter capacitor 76connected between the common point 74 and the center tap 68.

The feedback circuit 72 leads the amplifier output current through apair of feedback windings 78 and 80 each wound on a respective one ofthe magnetic cores 14 and 16 of the first amplifier stage 10, andthereby effectively nulls the control winding input signal. The feedbackcircuit also couples changes in the output signal through a capacitor 82and a resistor 84 to a negative feedback winding 86 which is woundaround both of the magnetic cores 54 and 56 of the second stage 12, andwhich serves to stabilize the amplifier output.

As in the previous stage 10 of amplification, the cores 54 and 56 alsoare provided with a short-circuited winding 88 which encircles both ofthese cores and serves to provide a low impedance path for the How ofharmonic signals. A particular advantage is that this Windingeffectively decouples the second stage 12 from the output circuit of thefirst stage 10, and thereby assures more stable operation of the overallamplifier.

Winding specifications for an amplifier constructed as described aboveand found to operate satisfactorily are as follows:

(1) Cores 14 and 16-Core material of the squarehysteresis typecomprising 3 mil tape, e.g. HYMU 80 as manufactured by MagneticsIncorporated under N0. 50,003-3D;

(2) Gate windings 18 and 20-1320 turns of AWG No. 34 copper wire with anelectrical resistance of 33 ohms each.

(3) Control winding 46-1000 turns of AWG No. 38 copper wire with anelectrical resistance of 150 ohms.

(4) Bias winding 48-500 turns of AWG No, 38 copper wire with anelectrical resistance of 104.5 ohms.

Short-circuited winding 52-500 turns of AWG No. 40 copper wire with anelectrical resistance of 108 ohms.

(6) Feedback windings 78 and 80-90 turns of AWG No. 34 copper wire withan electrical resistance of 2.5 ohms each.

(7) Cores 54 and 56-Core material of the squarehysteresis typecomprising 4 mil tape, e.g. Orthonol as manufactured by MagneticsIncorporated under N0. 50,0264A;

(8) Gate windings 58 and 60-2850 turns of AWG No. 32 copper wire with anelectrical resistance of 77 ohms.

(9) Control winding 36-200 turns of AWG No. 36 copper wire with anelectrical resistance of 26 ohms.

(l0) Short-circuited winding 88-7 turns of AWG No. 22 copper wire withan electrical resistance of approximately 0.03 ohm.

(11) Feedback winding 86-1000 turns of AWG No. 38 copper wire with anelectrical resistance of 200 ohms.

Figure 3 shows a modified amplifier adapted to accept A.C, input signalsand to produce bi-polar output signals in accordance with the phase ofthe input signal. This amplifier includes two separate amplifiersections generally indicated at 90 and 92 having their respective inputcircuits connected in series and their respective output circuitsconnected differentially.

Each of these amplifier sections includes a pair of toroidal cores 94,96 and 98, 100 with each pair of cores arranged in coaxial side-by-sideconfiguration. These cores are provided with respective gate windings102, 104 and 106, 108, the corresponding pairs of which are connected inbalanced full-wave output circuits as described with reference to Figurel. The gate windings are energized by a power transformer throughrectifiers 112, 114 and 116,118, and the respective output circuitsinclude load resistors and 122 which are connected together at a commonpoint 124.

The magnetic cores also are provided with control windings 126, 128 and130, 132 connected to input terminals 134 and 136. The first pair ofcontrol windings 126, 128 are connected together in parallel, as are thesecond pair of control windings 130, 132. However, the winding pairs areconnected in series relationship with respect to the input terminals 134and 136 so that the input current flowing through the sections 90 and 92will always be equal.

Bias windings 138 and 140 are wound around the cores and are suppliedwith D.-C. current by a rectifier power supply 142. A balancingpotentiometer 144 is connected across the power supply output to permita fine adjustment of zero balance between the two amplifier sections 90and 92.

The amplifier includes a pair of output terminals 146 and 148 connectedto remote ends of the load resistors 120 and 122 respectively so thatany difference in potential drop across the resistors will appear as anoutput voltage at these terminals. With zero input current through thecontrol windings 126, 128 and 130, 132, the amplifier is adjusted sothat equal currents will flow through these load resistors, andaccordingly the output voltage will be zero. With an A.C. input signalof a given phase, one of the load resistors will carry more current thanthe other, and an output voltage of corresponding polarity will beproduced. It the input signal phase is reversed, the other load resistorwill carry the greater current, and the output voltage polarity willaccordingly reverse.

With the control windings 126 and 128 connected in parallel as describedabove, these two windings together act as a short-circuited windinginsofar as the two magnetic cores 94 and 96 of the first amplifiersection 90 are concerned. Similarly, the control windings 130 and 132act as a short-circuited winding for the second section 92. Accordingly,these control windings serve the dual function of controlling the outputsignal of the magnetic amplifier and also absorbing harmonic componentsgenerated in the gate windings 102, 104, 106 and 108.

Each section 90 and 92 of the amplifier also is provided with acorresponding negative feedback winding 150 and 152 both of which areconnected in series with a currentlimiting resistor 154 across theoutput terminals 146 and 148. Whenever an output voltage appears acrossthese terminals, the resulting flow of feedback current aids instabilizing the amplifier operation.

It should also be noted that the Figure 3 arrangement can be used as aD.-C. amplifier by making appropriate changes to the polarity of thecontrol windings.

Although specific preferred embodiments of the invention have been setforth in detail, it is desired to emphasize that these are not intendedto be exhaustive or necessarily limitative; on the contrary, the showingherein is for the purpose of illustrating the invention and thus toenable others skilled in the art to adapt the invention in such ways asmeet the requirements of particular applications, it being understoodthat various modifications may be made without departing from the scopeof the invention as limited by the prior art.

I claim:

1. Magnetic amplifying apparatus comprising, in combination, saturablemagnetic material establishing first and second pairs of closed fluxpaths, first and second pairs of control windings each wound about acorresponding one of said flux paths, first circuit means connectingsaid first pair of control windings together in parallel to form ashort-circuited winding encircling said first pair of flux paths, secondcircuit means connecting said second pair of control windings togetherin parallel to form a shortcircuited winding encircling said second pairof flux paths, input circuit means connecting said first and secondpairs of control windings together in series relationship, first andsecond output winding means inductively coupled to said first and secondpairs of flux paths respectively, energizing circuit means includingrectifier means for feeding rectified A.C. current to said outputwinding means, first and second load elements connected to said firstand second output winding means respectively, and an output circuitcoupling said first and second load elements together ditferentiallywhereby any unbalance in the average current carried by said elementsproduces a corresponding output voltage.

2. A magnetic amplifier comprising, in combination, a pair ofcoaxially-positioned balanced toroidal magnetic cores each establishinga closed flux path, a pair of output windings each wound around arespective one of said toroidal cores, an alternating-current energizingcircuit arranged to feed current through said output windingsrespectively on alternate half-cycles of the AC. supply voltage, a loadelement connected in series with said energizing circuit to carry saidcurrent, control winding means surrounding both of said cores, andcircuit means establishing a short-circuited electrically-conductivepath surrounding both of said cores, said electrically-conductive pathbeing so disposed with respect to said cores that a current flowingaround said path will produce in said cores respective fluxes having thesame directional relationship with respect to the corresponding fluxesproduced in said cores by said output windings during the firinghalf-cycles thereof.

3. Magnetic amplifying apparatus for amplifying A.C. signals andcomprising saturable magnetic material defining first and second closedflux paths, first and second output windings inductively coupled to saidflux paths respectively, a full-wave A.C. energizing circuit includingrectifier means for feeding half-wave A.C. current to said outputwindings on opposite half cycles of the AC, supply, first and secondcontrol windings for said flux paths respectively, an input circuit forfeeding an A.C. control signal to both of said control windings, andcircuit means conductively connecting said two control windings directlyin parallel with each other and with said input circuit, to form ashort-circuited Winding encircling said flux paths; said controlwindings being wound in directions to provide, for said A.C. controlsignal, the same flux-directional relationship with respect to saidoutput windings during the conducting half-cycles of said outputwindings respectively, so that the magnitudes of the currents flowingthrough said output windings will vary in the same direction withchanges in amplitude of said A.C. control signal.

4. A magnetic amplifier comprising, in combination, a pair ofcoaxially-positioned balanced toroidal magnetic cores, 2. pair of outputwindings each wound around one of said cores, an AC. energizing circuitarranged to feed current through said output windings respectively onalternate half-cycles of the A.C. supply voltage, a load elementconnected in series with said energizing circuit to receive saidcurrent, control Winding means surrounding both of said flux paths, andcircuit means establishing a short-circuited electrically-conductivepath having first and second portions each at least substantiallysurrounding a respective one of said cores and together forming ashort-circuited winding encircling both or said cores, said first andsecond portions being so interconnected that a current flowing in agiven direction around said shortcircuited winding will produce in saidcores respective fluxes having the same directional relationship withrespect to the corresponding fluxes produced by said output windingsduring the firing half-cycles thereof.

5. A magnetic amplifier as claimed in claim 4, wherein said controlwinding means consists of first and second separate windings eachsurrounding one of said cores, said first and second separate windingsserving to define said first and second path portions respectively, saidcircuit means comprising a two-wire input circuit arranged to connectsaid first and second windings together to form said short-circuitedWinding.

References Cited in the file of this patent UNITED STATES PATENTS2,552,203 Morgan May 8, 1951 2,767,367 Black Oct. 16, 1956 2,792,541Markow May 14, 1957 2,832,037 Guth Apr. 22, 1958 OTHER REFERENCESElectronics, January 1954, pages 181-183, Magnetic Amplifier UsesConventional Inductors, by A. 1. Bennett, Jr., particularly Fig. 1.

Types of Magnetic Amplifiers, A Survey, by J. G. Miles, Fig. 16, pages10 and 11. Transcrip of paper delivered at AIEE Winter Meeting, N.Y.C.,J an. 24, 1951, publ. Engineering Research Associates, Inc, St. Paul,Minn, Arlington, Va.

Geyger: Magnetic Amplifier Circuits, publ. McGraw- Hill, First edition1954, page 115, Fig. 8.2, page 117, Fig. 8.4, page 143, Fig. 9.10, page175, Fig. 12.2.

Geyger: Magnetic Amplifier Circuits, published by McGraw-Hill, 1st. ed.,1954, page 177, Fig. 12.3.

